Electrochemical Insights into Copper Electrodeposition on Nd₂Fe₁₄B Grains: A Proof-of-Concept Study

This study explores Cu electrodeposition from a near-neutral sulphate bath onto Nd-Fe-B bulk and powder electrodes. The former served for the preliminary electrochemical tests, while the latter was used for Cu coating of the corrosion-sensitive powdery raw material. Cyclic voltammetry established the potential intervals for Cu deposition (at least −0.1 V and below) and the Nd-Fe-B oxidation (above −0.5 V). Cu electrodepositions were performed on both electrodes in potentiostatic mode for 30 s. Scanning electron microscopy/energy-dispersive spectroscopy showed that Cu deposited at high overpotentials (−1.05 and −0.5 V) had a dendritic structure mainly due to mass transport limitations. A chronoamperometric study on Nd 2 Fe 14 B powder electrodes at −0.25 V resulted in a positive current, indicating the Nd-Fe-B oxidation dominance. At −0.5 V, the current remained negative, but showed diffusion limitations. The latter was improved by using ultrasonic agitation, which resulted in a higher total negative charge and more uniform Cu deposits on Nd 2 Fe 14 B grains. Cu-coated Nd₂Fe₁₄B grains showed a mass magnetization decrease from 137 to 127 emu g −1 , corresponding to a ∼9% Cu mass increase determined via gravimetry. The study demonstrates successful Cu electrochemical deposition with no magnetization loss beyond the paramagnetic Cu phase, paving the way for grain-boundary engineering of novel Nd-Fe-B magnets.